Answer:
The Comma Johanneum, also known as the Comma Johannine, is a textual variant in regards to 1 John 5:7-8. The word comma simply means “short clause,” and Johanneum means “pertaining to John.” Without the “comma,” 1 John 5:7-8 reads, “For there are three that testify: the Spirit, the water and the blood; and the three are in agreement.” With the “comma,” 1 John 5:7-8 reads, “For there are three that bear record in heaven, the Father, the Word, and the Holy Ghost: and these three are one. And there are three that bear witness in earth, the Spirit, and the water, and the blood: and these three agree in one.” If the Comma Johanneum was originally part of 1 John 5:7-8, it would be the clearest and most direct reference to the Trinity in the entire Bible.

However, it is highly unlikely that the Comma Johanneum was originally a part of 1 John. None of the oldest Greek manuscripts of 1 John contain the comma, and none of the very early church fathers include it when quoting or referencing 1 John 5:7-8. The presence of the Comma Johanneum in Greek manuscripts is actually quite rare until the 15th century A.D. It is primarily found in Latin manuscripts. While some of the Latin manuscripts containing the Comma Johanneum are ancient, the Comma Johanneum did not appear in the original Latin Vulgate written by Jerome.

In the 16th century, when Desiderius Erasmus was compiling what became known as the Textus Receptus, he did not include the Comma Johanneum in the 1st or 2nd editions. Due to intense pressure from the Catholic Church and others who wanted it included because of its support for trinitarianism, Erasmus included the Comma Johanneum in later editions of the Textus Receptus. His decision resulted in the Comma Johanneum being included in the King James Version of the Bible and later in the New King James Version. None of the modern Greek texts (UBS 4, Nestle-Aland 27, Majority Text) contain the Comma Johanneum. Of all the modern English translations, only the New King James Version includes the Comma Johanneum.

While it would be convenient for there to be an explicit statement confirming the Trinity in the Bible, it is highly unlikely that the Comma Johanneum was originally a part of 1 John. Some ancient scribe, either intentionally or accidentally added it to a Latin manuscript, and then that addition was copied thousands upon thousands of times. This eventually resulted in the Comma Johanneum appearing in the vast majority of Latin manuscripts. Whatever the scribe’s motives, it is absolutely wrong to add to God’s Word. While what the Comma Johanneum says is true, it is not a God-breathed statement and does not belong in the Bible. The doctrine of the Trinity is taught and implied in many other biblical passages. If God thought an explicit mention of the Trinity was necessary, He Himself would have made sure it was in His Word.